Revert "Allow system server to set persist.traced.enable"

This reverts commit 6f2040f8.

Reason for revert: not needed anymore after ag/3773705
This was meant to allow system_server toggling the property on/off.
Later we realized that we needed a separate property for that 
(see discussion in b/76077784) and system server happens to
have already permissions to write to sys.* properties even without
this CL.
Reverting because at this point this creates just unnecessary clutter.

Change-Id: Ia73d000aad3c4288a5652047dfe10896e231b0b1
Test: perfetto_integrationtests
Bug: 76077784